This application is based on an application No. 2000-297621 filed in Japan, the content of which is incorporated hereinto by reference.
1. Field of the Invention
The present invention relates to a crystalline silicon particle, a method of producing the same, and a photoelectric conversion device using the crystalline silicon particle produced by the method.
2. Description of the Related Art
Advent of a next-generation, low-cost solar cell that allows the quantity of silicon material to be small has been eagerly awaited. As one of such photoelectric conversion devices, a photoelectric conversion device in which granular or spherical crystalline silicon particles are used has been known. (Refer to U.S. Pat. No. 4,691,076)
The method of producing the crystalline silicon particles used in such a photoelectric conversion device is as follows: silicon particles having irregular shapes are used as the raw material and dropped inside a drop tube. While falling inside the drop tube, the silicon particles pass through an inductively coupled plasma torch that has been generated inside the drop tub so as to be fused and formed into spherical monocrystal silicon particles (Refer to U.S. Pat. No. 6,074,476).
However, the spherical monocrystal silicon particles produced by such a conventional production method suffer defects remaining inside the particles, which causes the photoelectric conversion efficiency to drop.
Accordingly, it has been impossible for conventional methods to produce crystalline silicon particles that can be suitably used in a photoelectric conversion device.
It is an object of this invention to provide a crystalline silicon particle that makes it possible to obtain a photoelectric conversion device having excellent characteristics, a method of producing the same, and a photoelectric conversion device using the crystalline silicon particle.
The crystalline silicon particle according to the present invention contains hydrogen at a concentration of 1xc3x971016-1xc3x971020 atoms/cm3. The hydrogen combines with dangling bond in the crystalline silicon particle so as to inactivate defects at crystal grain boundaries or within the crystal grain. As a result, it is possible to prolong the lives of carriers in the semiconductor and improve the photoelectric conversion efficiency.
A method of producing a crystalline silicon particle according to this invention comprises the steps of: generating plasma by ionizing a plasma generating gas having an inert gas and hydrogen gas mixed together in a prescribed ratio; passing a silicon material through the plasma; and producing a crystalline silicon particle containing hydrogen at a concentration of 1xc3x971016-1xc3x971020 atoms/cm3.
According to this method, it is possible to easily add hydrogen having a concentration within a prescribed range to the crystalline silicon particle by blending hydrogen with the plasma generating gas.
Crystalline silicon particles tend to have a great deal of defects especially when produced by a gravitational falling method in which the crystalline silicon particles are rapidly crystal-grown. However, even in such a case, the method of producing a crystalline silicon particle according to the present invention can inactivate the defects by adding hydrogen to the crystalline silicon particles.
In addition, it is also possible to determine the conductivity type of the crystalline silicon particle by adding a gas containing an impurity element to the plasma generating gas.
The photoelectric conversion device using the crystalline silicon particle of the present invention comprises: a substrate; numerous first-conductivity-type crystalline silicon particles deposited on the substrate being in contact with the substrate; an insulator formed in clearances among the crystalline silicon particles on the substrate; and an opposite-conductivity-type semiconductor layer formed over the crystalline silicon particles and the insulator for forming a pn-junction between the layer and the crystalline silicon particles, wherein the crystalline silicon particles contain hydrogen at a concentration of 1xc3x971016-1xc3x971020 atoms/cm3. Having the structure above, the present invention can provide a photoelectric conversion device with high photoelectric conversion efficiency.